1. Field of the invention.
The present invention relates to the use of coherent energy pulses to improve the properties of a solid material by providing shock waves therein and in particular methods and apparatus for remotely directing the pulse of coherent energy.
2. Description of the related art.
Laser shock processing involves directing a pulse of coherent radiation to a piece of solid material to produce shock waves therein. The produced shock wave causes compressive residual stresses to form within the solid material. These compressive residual stresses improve the fatigue properties of the solid material.
Currently, laser shock processing utilizes two overlays: a transparent overlay (usually water) and an opaque overlay (usually an oil based paint or black plastic tape). During processing, a laser beam is directed to pass through the water overlay and is absorbed by the black paint, causing a rapid vaporization of the paint surface (plasma creation) and a generation of a high-amplitude shock wave. The shock wave cold works the surface of the part and creates compressive residual stresses, which provide an increase in fatigue properties of the workpiece. A workpiece is typically processed by processing a matrix of overlapping spots that cover the fatigue critical zone of the part.
Currently, laser shock processing apparatus are mounted in a fixed or stationary location. The laser and the laser beam pathway are held in a fixed position directed toward a workpiece located in an immobile or stationary processing station. In order to laser shock process a workpiece, the workpiece must be placed within the stationary processing station and aligned within the laser beam pathway. As a result of the workpiece having to be located within the processing station, the size or dimension of the workpiece to be processed is thereby limited; the workpiece must fit within the finite space of the stationary processing station.